In the area of small electrical devices it is customary to use electrical energy stores that are separable from the small device in order to be recharged. During the charging process, an additional energy store may be inserted into the small device such that the latter may continue to be operated during the charging process. Frequently it is also possible to use the energy store interchangeably in different small electrical devices, for example in a battery-operated screwdriver and in a lamp.
Known energy stores include a control unit, which monitors both a charging process as well as a discharging process of the energy store. This is to improve an energy management and reduce the danger of damaging or destroying one of the devices or the energy store due to incorrect charging or discharging. The control unit is developed as an electronic circuit and monitors parameters such as one or more cell voltages of an accumulator of the energy store as well as, if applicable, one or more cell temperatures. For the purpose of exchanging information, the control unit may be connectable to another control unit, which is situated in the small device or the charger. The control unit is normally operated by the electrical energy of the accumulator, components especially being used in the construction of the control unit that have a low power consumption or a special power-saving mode (“sleep mode”) in order to avoid discharge when storing the unit.
European Published Patent Appln. No. 1 337 025 shows a charger for an electrical energy store, which is electrically disconnected from a supply mains if no energy store is inserted into the charger, in order to minimize an energy consumption of the charger outside of the charging operation.
A current consumption of the control unit, however, occurs even when the energy store is not connected to a device. In the course of a longer storage period, the performance of the energy store may be impaired by the discharging of the control unit. In unfavorable circumstances, the accumulator of the energy store may even be exhaustively discharged by the control unit and thus damaged or even destroyed.